It is well known that when water is boiled in a kettle, solid scale tends to form inside the kettle. It is known for a single filter to be located in the kettle spout to prevent at least the large bits of scale leaving the kettle and entering, for example, a drink being made with water which has been boiled in the kettle. Such filters can become quickly clogged and are often difficult to remove and clean.
GB Specification 2308055 describes a single filter element, screw fitted into the open end of a kettle.